theres on the manual something about focal points/zoom/ distance of the object.
and it says that in a certain way it will not focus because the lens cant handle focus... sorry i have to look in the manual what the precise description is....

Perhaps if the scene is too dark, the camera is having trouble to focus on your target. That is quite normal behavior for any camera. Most cameras are equiped with a focus assist facility. I think the E520 uses flash strobes to assist you while focussing. That means that your camera quickly fires a sequence of flashes to light the scene. It might be worth a try using this function.